Magnetic susceptibility of the Chinese loess-palaeosol sequence: environmental change and pedogenesis

Abstract: Pronounced differences in concentration, alignment and grain-size distribution of the magnetic minerals have been identified between loess and palaeosol samples from the section at Xifeng (Central Chinese loess plateau). Superparamagnetic magnetite formed in situ plays an important role in controlling magnetic low field susceptibility. The variable brown-red colouration of the Ioess-palaeosol sequence is due to a significant hematite component produced by pedogenesis. The magnetic fabric of the palaeosols i weaker than that of the loesses. This is taken as evidence that the formation of ultrafine ferromagnetic minerals by pedogenesis the most likely explanation for the observed susceptibility enhancement i palaeosols (4 to 10 times higher than in loesses). It is argued that variations of frequency dependent susceptibility are sensitive recorders of second order palaeocli-matic variations during glacial periods, whereas bulk susceptibility seems to be an appropriate measure of palaeoclimate change during interglacial periods. Extremely thick loess of mainly aeolian origin covers large parts of northern China. The loess stratigraphy typically consists of alternating loess and palaeosol layers which were deposited during the last 2.5 Ma. The loess is formed b